Do you have history of prolonged or frequent squatting or cross leg sitting recently like in some event or marriage
It is probably due to muscle fatigue. In elderly age group ,such symptoms indicates osteoarthritis which is pain due to wear and tear of knee joint cartilage,however at 28 age, osteoarthritis is less likely.
Next Steps
Get a knee X ray done in standing position.
start analgesics after in clinic consultation with an orthopaedician
Health Tips
avoid squatting, climbing stairs and sitting cross leg. drink plenty of fluids